The present invention relates to an arrangement for the application of pressure on a packing machine which comprises a stepwise rotatable mandrel wheel with radial mandrels for supporting and positioning of packing container blanks to form the bottom portion of containers made from the blanks.
Packing containers of the so-called gable-top type are used at present as non-returnable packages for a number of produces, above all liquid foods such as milk or juice. The packing containers are manufactured from a foldable, semi-rigid packing laminate which generally comprises a carrier layer of fibrous material, coated on both sides with thermoplastic material which on the one hand provides good liquid-tightness, and on the other hand makes possible hot-sealing of the packing laminate. The packing laminate is divided into individual sheets which by means of a longitudinal, liquid-tight seal are converted to tubular blanks of substantial square cross-section. The blanks are provided with suitable crease lines so as to delimit wall panels for the side walls as well as top and bottom wall panels which by means of folding and sealing can be converted to a liquid-tight top and bottom respectively. This conversion of the tubular blanks takes place, like the filling with contents, in a packing machine where the tubular blanks are provided with a bottom by the folding of bottom wall panels along the crease lines and sealing the panel so as to form a plane bottom. As result, the blanks are given a fillable from and the desired quantity of contents can be introduced. After the filling the top of the packing container is formed by folding of the top wall panels and subsequent hot-sealing. A packing machine of this type is shown in Swedish patent no. 361.857.
In the manufacture of packing containers in a machine of the aforementioned type the forming and sealing of the bottom of the packing container blank generally are carried out in the following manner: The tubular blank is placed on a mandrel of square cross-section and is maintained in such a position that the bottom folding panels located at the bottom end of the blank extend outside or beyond the free end of the mandrel. The mandrel is arranged, together with a number of mandrels of the same sort, radially on a mandrel wheel which is stepwise rotatable so that a blank placed on a mandrel can be moved between different processing stations. After a blank has been placed on a mandrel while the mandrel is in a loading station, the mandrel wheel is turned so that the actual mandrel with the blank stops in a heating station where a hot-air furnace or some other suitable heating device heats the thermoplastic layer on the parts of the packing container blank which extend outside or beyond the mandrel end and are to be sealed to one another so as to form the bottom when the heating the mandrel and the blank are moved to a sealing station. During this movement a successive folding of the bottom folding panels takes place, so that the panels partly overlap one another and form a plane bottom. The bottom is pressed down and is sealed with the help of pressure devices which are displaceable so that they can be pressed with a predefined force against the bottom wall panels and the mandrel end lying or positioned behind the bottom. Since the total surface of the bottom is relatively large, very high compressive forces arise in the sealing process, which brings about great stresses on the axle of the mandrel wheel as well as on its bearing arrangement in the machine frame. These machine components, therefore, have to be fairly largely dimensioned.
This, of course, is undesirable, and it is attempted in modern machine designs to distribute and reduce especially stresses on the bearing of the mandrel axle with the help of tie rods, arranged between the machine frame and the projecting part of the mandrel axle supporting the mandrel wheel. It is a disadvantage of such an arrangement that when the bottom portion of a container is pressed down a certain movement and oblique stressing cannot be wholly avoided, which makes necessary a flexible support of the pressure applying element. This is achieved with the help of rubber grommets which, however, impair the precision of the arrangement. The arrangement, moreover, is applicable only to those types of machines where the application of pressure is performed with the help of the sort of elements which do not require to be directly mechanically connected to the driving arrangement of the packing machine, that is to say piston and cylinder units of pneumatic or hydraulic type.
It is generally desirable that in a machine of the abovementioned type it should be possible to utilize a mechanical, cam-controlled pressure application, since this permits increased accuracy as well as higher operating speed. At the same time a reduction of the stress on the mandrel axle and its associated bearing is particularly desirable, especially if this can be achieved without oblique stress and without flexible suspension of the unit.
It is an object of the present invention to provide a pressure application arrangement for a packing machine with mandrel wheel, this arrangement being of a simple design, reliable function and long working life.
It is a further object of the present invention to provide an arrangement with mechanical pressure application, where the compressive forces arising, and the reactive force following thereupon, can be taken care of without the mandrel axle and its associated bearings being subjected to excessive stresses.
Finally, it is a further object of the present invention, to provide a pressure application arrangement which is of high precision, even during prolonged operation and lacks the disadvantages which similar, previously known, designs have been subject to.
These and other objects have been achieved in accordance with the invention in that an arrangement for the application of pressure on a packing machine which comprises a stepwise rotatable mandrel wheel with radial mandrels for the receiving, supporting and position of packing container blanks and the formation of containers having bottom portions from the blanks. The machine comprises an axle with eccentrically arranged portions, the axle being connected on the one hand to pressure devices so as to co-operate with the mandrels and on the other hand, to devices absorbing tensile forces which are connected to the mandrel wheel.